geofelt :
1600 ram is better binned normal 1.5v ram that can operate at 1600 with 1.65 volts.
This isn't always true, sometimes you can do better than that! For exaple, the 1600 GSkills I have run at 1.5V.
mushroomking :
I'm glad you mentioned it but it says I can use 1600/1333/1066 without overclocking, 2200 with overclocking. So off that just curious what makes you think I cant use the 1600?
Before I launch into a detailed explanation let me say a couple things. First, if you haven't read this review yet you should give it a read, it compares different memory speeds and is very informative, especially the conclusions (but if you jump to the end you'll miss some of the meat):
http://www.tomshardware.com/reviews/core-i7-870-1156,2482.html
Second, even if you don't plan on OCing, there can still be very good reasons to get 1600 MHz RAM. One of the best reasons - sometimes its cheaper than similar 1333 MHz RAM. Sometimes 1600 RAM can be run at 1333 with tighter timings. Sometimes it can be run with lower V when set to 1333. 1600 RAM is nothing but 1333 RAM that the manufacturer certifies as OCable. I kinda like the way
this article on value RAM puts it:
Performance guarantees are nice, but paying someone else to validate an overclock can put a big dent in the value a mid-priced system represents. After all, most builders don't pay extra for a CPU that has been validated by a third party to run at higher speeds, yet very few overclocking enthusiasts seek better value by risking the chance of a “poor yield” in exchange for a lower price. We willingly take that small risk with processors, so why not apply the same principle to RAM?
Now for the answer to your question: What makes [me] think that [you] can't use the 1600?
A: You can use the 1600. You just can't run it at 1600 without OCing or making other tradeoffs.
With an i5 750 you cannot run RAM any faster than 1333 with effectively OCing your computer. You can often turn on XMP in BIOS, and many people recommend doing this, but this changes your BCLK which also affects your CPU speed. It might, as a side effect, end up turning off functionality such as Turbo, EIST, sleep states. You can usually turn those back on but you have to specifically do it. This differs from motherboard to motherboard.
To provide more detail on why memory multipliers and XMP affect your CPU, we need to discuss how the RAM and CPU speeds are determined. There are 3 important settings: BCLK, Memory Multiplier, and the CPU Clock Ratio.
RAM Speed = BCLK x Memory Multiplier
CPU Speed = BCLK x CPU Clock Ratio
By default, the 1156 socket chips run with a BCLK of 133. The CPU and RAM attain different speeds by using different multipliers.
The Max Memory Multiplier that is available to the i5 750 chip (and the i5 and i3 Clarkdale chips) is one that allows RAM to reach a speed of 1333 MHz at default BCLK. Doing the math, this is basically 10 (some boards treat it differently, but fundamentally it can be thought of as 10) because 133 BCLK x 10 Memory Multiplier = 1333 MHz. This is the max frequency RAM can run at with the i5 750 without OCing.
The Max Memory Multiplier that is available to the i7 8xx chips is one that allows RAM to reach a speed of 1600 MHz at default BCLK. Doing the math, this is essentially 12 because 133 BCLK x 12 Memory Multiplier = 1600 MHz.
The i5 750 runs with a default CPU Clock Ratio of 20. This gives it it's default CPU speed of 133 BCLK x 20 CPU Clock Ratio = 2.66 GHz. When XMP is turned on for 1600 MHz RAM, the BCLK is usually changed to 160 (this could differ between boards as well, but in my experience and what's been reported the BCLK changes to 160). Remember, the max memory multiplier available to the i5 750 is 10, so to hit 1600 MHz the motherboard must change the BCLK to: 1600 / 10 = 160.
As a result of this BCLK change, the CPU speed changes. If the CPU Clock Ratio did not change your CPU would be OCed to 20 x 160 = 3.2 GHz. Most (if not all) motherboards would deem this too dangerous to allow when all a user does is enable the XMP profile. So, the boards drop the CPU Clock Ratio in response to the raised BCLK. Based on what I've seen around the forum, most (all?) boards will drop the CPU Clock Ratio to 17. This means your CPU is running at a speed of 17 * 160 = 2.72 GHz.
Gigabyte treats this as an OC and from what I've been told around this forum other motherboards do the same. If you have left other settings as is, the motherboard will disable Turbo, EIST, and Sleep States. This is the trade-offs I've been talking about. These functions can be turned back on, but you have to go in and flip the settings from "Auto" to "Enabled" (the setting may differ for Asus). "Auto" means the motherboard decides whether or not to allow these functions. By setting it to "enabled" you ensure that they are always available. Furthermore, if you want to keep Turbo you have to change your CPU clock ratio back up to 20.
Of course once you have XMP turned on and your BLCK gets bumped up to 160, Turbo will run your machine even faster. When Turbo kicks in, the CPU Clock Ratio changes. For example, with one core of an i5 750 active Turbo might raise the CPU Clock Ratio as high 24. This gives a stock CPU a max speed of 133 BCLK x 24 CPU Clock Ratio = 3.20 GHz. But with XMP on and a BCLK of 160, your new max speed is 160 x 24 = 3.84 GHz. You'll want to test your system for stability running at these settings. Keep an eye on Voltage and heat.
Putting this all together, at default/stock we have:
BCLK = 133
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 20
RAM Speed = BCLK x Memory Multiplier = 133 x 10 = 1333 MHz
CPU Speed = BCLK x CPU Clock Ratio = 133 x 20 = 2.66 GHz
When Turbo kicks in (for example, let's say it is at it's max):
BCLK = 133
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 24
RAM Speed = BCLK x Memory Multiplier = 133 x 10 = 1333 MHz
CPU Speed = BCLK x CPU Clock Ratio = 133 x 24 = 3.20 GHz
With 1600 RAM and XMP on
BCLK = 160
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 17
RAM Speed = BCLK x Memory Multiplier = 160 x 10 = 1600 MHz
CPU Speed = BCLK x CPU Clock Ratio = 160 x 17 = 2.72 GHz
With 1600 RAM and XMP on, when Turbo kicks in, assuming you turn it back on and OC your rig by raising your cpu clock ratio back to 20:
BCLK = 160
Memory Multiplier (effectively) = 10
CPU Clock Ratio = 24
RAM Speed = BCLK x Memory Multiplier = 160 x 10 = 1600 MHz
CPU Speed = BCLK x CPU Clock Ratio = 160 x 24 = 3.84 GHz
As I said before, you're overclocking now and you'll want to test your system for stability running at these settings. Keep an eye on Voltage and heat. Also, although I used XMP as an example you could accomplish the same thing by setting BCLK, the memory multiplier, timings and voltage by hand.
.
.
Facebook
Twitter
Instagram